The present invention relates to apparatus or systems for transmitting modulated RF signals to a monitoring station, especially signals serving to indicate the presence of a defect or hazard in the system. More particularly, the apparatus of the present invention is contemplated for installation in a railway system for reporting "hot bearing" or other defects to a locomotive cab or to a wayside station.
One particular environment in which the present invention may be considered for use is that disclosed in U.S. Pat. No. 4812826. In that patent, there is shown an electronic module in FIG. 3 that may be utilized in the detection of hot/bearings. When the interior of the bolt reaches a prescribed temperature due to heat being developed in the wheel bearing, the expansive effect on a wax motor causes the module to be energized and an antenna to be suitably deployed so as to transmit a modulated signal, preferably in identifiable coded form, as a warning signal that a beating may be defective.
In the particular context of U.S. Pat. No. 4812826, reliance is placed on the wax motor's response to the elevated temperature, such that the wax expands and the antenna becomes deployed for broadcast purposes. However, phase change in the wax motor is not an instantaneous event since there is a slope in its pressure/temperature curve. Accordingly, without preventive steps, it is possible for the wax motor to build enough pressure to close the switch which activates the electronic circuitry, but not so much that the antenna is fully deployed. Such an equilibrium could theoretically exist indefinitely. This potential problem would dictate the provision of a lockout mechanism and thus would add hardware complexity.
Accordingly, it is a principal object of the present invention to circumvent the aforenoted potential problem by providing a quite different approach to the issues of activation of the electronic circuitry and deployment of the system's antenna.
Lithium batteries of the reserve cell type retain the electrolyte chemistries in a glass ampule. This eliminates shelf-life degradation problems that affect "active" lithium batteries. Thus, reserve cells offer a substantial extended life expectancy advantage because they can remain in the idle state, and hence, do not suffer the self-discharge/degradation of active cells which tends to increase greatly with temperatures. Since growing numbers of commercial applications are steadily driving the volumes of reserves produced to much higher levels, their cost has been decreasing.
A reserve electro-chemical cell that is activated by high acceleration forces acting on a frangible ampule is disclosed in U.S. Pat. No. 4800141. However, such disclosure in no way refers to the objects to be obtained by the present invention as aforenoted.